The invention relates generally to floating connector subassemblies useful for optical cable connectors. More particularly, this invention relates to subassemblies and optical cable connectors that are configured to floatingly align and tune mated ferrules within the connectors. Even more particularly, this invention relates to a connector subassembly that includes a plug housing having an inner surface with slanted or sloped alignment features and a ferrule holder. The connectors may be used, for example, to join segments of optical cables and to connect an optical cable with an optical device, such as, for example, radiation sources, detectors, repeaters, switches, attenuators, and the like.
Various types of connectors have been developed for connecting optical cables to optical system components, such as, for example, to join segments of optical cables and to connect an optical cable with an optical device, including, radiation sources, detectors, repeaters, switches, attenuators, and the like. Numerous factors influence the design of such connectors, including the diameter and makeup of the optical fiber used in the cable, the environment into which the cable and connector are placed, the space available for connection and the number of connections required in a given location, to name but a few. Standardized optical cable connector designs currently in common use include the SC-type, FC-type, ST-type, and RJ-type connectors.
Regardless of the optical cable connector design selected for a particular application, the central function of an optical cable connector is to maintain the optical fiber end in precise position relative to another fiber or another system component so as to maximize the signal strength as the light passes through the connection (i.e., minimize insertion losses). Even slight mispositioning of a fiber can contribute to insertion losses. In the past, industry had accepted some transmission loss due to misalignment. However, growing use of optical cables for communicating data demands near 100% transmission and reception capability and thus, minimal insertion loss. The degree of insertion loss in coupling two fibers is generally dependent on factors, such as, for example, the alignment of the fiber central axis at the ends, the width of the gap between the ends, and the optical surface condition of the ends.
To couple virtually all of the light from one fiber to another fiber is a particularly challenging task because the light carrying regions or xe2x80x9ccoresxe2x80x9d of optical fibers are quite small. For example, in single mode optical fibers, the core diameter is about 8 microns. Thus, the very small end surface of the core must not only be precisely prepared, but must also be precisely located, both to tolerances in the range of fractions of microns, to achieve low insertion loss.
Another function of the optical cable connector is to provide mechanical stability and protection to the junction and its working environment. Stability and junction protection is generally a function of connector design. Bulkier designs may provide more stability, but may disadvantageously take up more space and cost more than other designs.
In a connection between a pair of optical fiber connectors, an optical fiber extending from a center of an end face of a ferrule is butted together with an end face of another ferrule and light travels from one optical fiber to the other along the central axes of the two optical fibers. One such arrangement using an LC connector is illustrated in U.S. Pat. No. 5,481,634.
Often, a xe2x80x9cfloatingxe2x80x9d arrangement is provided, wherein the two ferrules, once butted together, can float as a unit relative to the plug housings due to springs present in the plug housings. The butted ferrule ends are typically held in alignment by a sleeve covering both ends. Such floating arrangements are beneficial in that the ferrules can be joined together as an aligned unit without regard to any small misalignments or imperfections in the other connector elements. Thus, all connector elements need not be manufactured to extremely tight tolerances to achieve a well-aligned pair of ferrules and fibers, so long as the ferrules and certain alignment elements (e.g., the sleeve) are precisely manufactured and assembled.
Any radial eccentricity of a fiber within a ferrule (i.e., when a fiber""s central axis is spaced from the ferrule""s central axis) may be compensated for by xe2x80x9ctuningxe2x80x9d the ferrule by orienting the eccentricity in a given direction relative to its ferrule holder and/or plug housing. When the ferrule is connected to another ferrule, having both ferrules tuned in the same direction may reduce insertion loss by improving alignment if the fiber positioning within each of ferrules is within certain tolerances.
Some connectors use a straight (i.e., substantially rectangular, radially extending) key and groove feature to tune a ferrule relative to a plug housing. In such case, a substantially rectangular key extends from the plug housing into a substantially rectangular groove in a ferrule holder. Due to the substantially rectangular and radially extending complimentary shapes of the key and groove, the ferrule""s ability to compensate for any misalignments between the ferrule and the plug housing inner surface is limited. Thus, by maintaining precise tuning and alignment of the ferrule relative to its plug housing, the ferrule has little if any ability to float. By loosening the fit of such a key structure, for example by making the key smaller or the groove bigger, the precision of the tuning and alignment of the ferrule relative to its plug housing suffer, potentially defeating the purpose of the key and groove. Thus, a trade off exists between the precision of the floating capability and the precision of the tuning and alignment capability in available connectors. At present, mating components of available tunable connectors typically have used relatively tight tolerances, which in turn reduces the ability of the ferrule to float. In addition, conventional connector designs fail to include means to further minimize or compensate for alignment errors and manufacturing inaccuracies that would otherwise result in insertion losses.
Accordingly, it is an objective of this invention to provide a connector subassembly and a related connector having a floating capability and a tuning and aligning capability, wherein the component parts of the connector subassembly and connector are simple, reliable, and economical to manufacture, assemble, and use. Other objectives and advantages of the invention will be apparent from the following description and the attached drawings, or can be learned through practice of the invention.
According to an aspect of the invention, a connector subassembly includes a plug housing and a ferrule holder that provide floating capability and tuning and alignment capability of a ferrule. The connector subassembly includes a plug housing having an inner surface that defines a cavity extending longitudinally therethrough. The plug housing defines a forward opening in communication with the cavity for receiving an optical fiber extending into a ferrule and a rearward opening in communication with the cavity and configured for the optical fiber and the ferrule to extend substantially axially. The plug housing inner surface further defines a key extending into the cavity. The key defines a height along the plug housing inner surface that extends in a radial direction and decreases in a direction axially away from the rearward opening. The ferrule holder includes an inner surface configured to hold the ferrule and an engaging surface configured to mate with and engage an engaging surface of the plug housing, wherein the engaging surface of the plug housing is at least a portion of the inner surface of the plug housing. The outer surface of the ferrule holder defines a longitudinally extending axial groove for slidably receiving the key so that the ferrule holder is increasingly radially movable relative to the inner surface of the plug housing as the ferrule holder moves relative to the plug housing in a direction axially away from the rearward opening.
The cavity of the plug housing includes a forward cavity in communication with the forward portion. The forward cavity may be substantially conical and may define a circular cross-section decreasing radially in a direction axially toward the rearward opening. The ferrule holder engaging surface is configured to mate with and engage the plug housing engaging surface and thus, at least a portion of a forward end of the outer surface of the ferrule holder may also be substantially conical and decrease radially in a direction axially toward a rearward end of the ferrule holder.
The ferrule holder may define a radially extending stop portion disposed proximate to the forward end of the outer surface of the ferrule holder, and the plug housing inner surface may define a complimentary stop portion, the groove extending axially across at least a portion of the ferrule holder stop portion.
The key may have a cross-section including a rounded tip. The groove may have a generally flared cross-section, which more particularly may be generally v-shaped. It is to be noted that the shapes of the key and the corresponding groove may be altered without losing the functionality of this invention. For example, the key may have a cross-section including a semi-circular, rounded, or rectangular tip, and the groove may have a corresponding matable cross-section. In addition, the key and groove combinations in the disclosed embodiments may be replaced by other connection means furnishing the same function.
The plug housing may optionally include at least two keys disposed circumferentially about the plug housing inner surface, and the ferrule holder may then include at least two grooves disposed about the ferrule holder engaging surface, each of the grooves slidably receiving a respective key. The at least two keys may be disposed nonsymmetrically circumferentially about the plug housing inner surface.
The plug housing inner surface may optionally include a planar aligning section and the outer surface of the ferrule holder may then include a planar aligning section, the planar aligning sections being engageable with each other. At least two planar aligning sections may be provided on each component.
A compression spring element may be disposed within the plug housing for urging the ferrule holder in a direction axially toward the rearward opening.
According to another aspect of the invention, the connector subassembly includes a plug housing having an inner surface with at least two orienting elements disposed thereon and a matable ferrule holder having an outer surface with at least two orienting elements disposed thereon. At least one of the orienting elements of the plug housing inner surface may include a second key, and at least another of the orienting elements of the ferrule holder may then include a second groove for slidably receiving the second key. Alternately or in addition, at least another of the orienting elements of the plug housing inner surface may include a planar aligning section, and at least another of the orienting elements of the outer surface of the ferrule holder may then include a planar aligning section engageable with the plug housing inner surface planar aligning section.
According to another aspect of the invention, a spring element is disposed within the plug housing and urges the ferrule holder in a direction axially toward the rearward opening. A crimp body is attached to the plug housing so as to compress the spring element. A boot is attached to the plug housing via the crimp body and is disposed about a portion of the optical fiber. In a preferred embodiment, the boot is a flexible boot; however, rigid boots may be used in alternate embodiments. The connector may also include a tube disposed about a section of the optical fiber and secured to the ferrule holder. It is to be noted that the arrangement of the spring element, crimp body, boot, and tube may be altered without losing the merit of this invention.